1. Field of the Invention
This invention generally relates to digital recording, playing, and playback of previously recorded audiovisual (A/V) signals in a digital system. This invention more particularly relates to a method and apparatus for efficiently identifying MPEG picture coding types in DSS transport packets received in digital television or recording systems, without having to parse and evaluate each DSS transport packet.
2. Description of Related Art
Conventional communication systems exist for recording broadcast audiovisual signals. Particularly, various digital VCRs are known that record an off-air broadcast and later playback the previously recorded program. These conventional communications systems may include a receiver for receiving and processing transmitted waveforms. One type of receiver is part of a “wireless digital television” system known commercially by the trade name DSS. The DSS system, which is utilized by the DIRECTV broadcast service, allows consumers to receive directly in their homes over 175 television channels broadcast from a pair of powerful satellites.
The receiver includes a satellite dish connected by a cable to an integrated receiver/decoder unit (IRD), hereinafter set top box or STB. The satellite dish is aimed toward the satellites, and the STB is connected to the user's television in a similar fashion to a conventional cable-TV decoder.
On the transmission side, video, audio, and related information data signals are digitally encoded into a packetized data stream called a DSS transport stream using a number of algorithms, including convolutional error correction. The encoded data stream is then punctured to reduce bandwidth requirements, modulated to Ku-band frequency, transmitted to the satellite, and relayed from the satellite to the 18-inch satellite dish. The satellite dish shifts the Ku-band signal down to an L-band signal that is transmitted through the cable to the STB.
In the STB, front-end circuitry receives the L-band signal and converts it to the originally transmitted digital data stream of video, audio, and related information signals. The digital data stream is fed to video/audio circuitry such as transport processor and video/audio decoders that perform the main video/audio processing functions such as de-multiplexing and decompression. A micro-controller controls the overall operation of the STB, including the selection of parameters, the set-up and control of components, channel selection, viewer access to different programming packages, blocking certain channels, and many other functions. The compression and decompression of packetized video and audio signals may be accomplished according to the Motion Picture Expert Group (MPEG) standard for performing digital video/audio compression. Thus, the STB unit typically includes an MPEG-1 and/or MPEG-2 video/audio decoder in order to decompress the received compressed MPEG video/audio that is in the received DSS transport stream.
In general, digital video and audio signals can be broadcast, processed, and recorded with a high degree of quality. In order to take better advantage of the high quality associated with digital video/audio, digitally-based peripheral devices, such as digital video cassette recorders (DVCR's) and digital video disks (DVD's), have been developed to receive and process video/audio in a digital format. The present invention relates to a method and apparatus for receiving broadcast entertainment-type data, such as packetized digital video, audio, data, and control signals received in a direct broadcast satellite (DBS) system, and for effectively recording the received data on a device such as a digital video recorder (DVR).
Within these packetized transport streams resides data that, when de-multiplexed at the STB, transforms into a group of pictures, or GOP. A GOP consists of coded pictures. A coded picture may be a frame or field. For progressive video, a picture is identical to a frame while for interlaced video; a picture refers to a frame, or the top field or the bottom field. A typical GOP may contain one I-picture, which is the anchor picture or intra-coded picture of the GOP, in 15 pictures of video. The P-pictures are single directional predictive pictures which are dependent on the I picture (i.e., the P pictures typically show changes in the basic overall image, like cloud cover changes in an image of a city skyline, for example). The B pictures are bi-directional pictures that provide for high compression (they have the highest compression ratio in the GOP). For example, a typical GOP may include I, P and B pictures in some order, such as I B B P B B P B B P B B P B B. These are actually different pictures of a subject image, hence group of pictures or GOP.
Current digital video recorders (DVRs) include some type of transport processor to process the received DSS transport packets from any of a cable, satellite, video-on-demand or other commercial video source. Known as a transport packet processor or simply “transport processor”, this processor must be able to identify the presence of a picture coding type, in order to facilitate DVR playback modes, and especially trick modes. This is because to initiate trick modes such as fast rewind, reverse playback, fast forward, instant replay, slow motion and frame-by-frame (or field-by-field) display for example, all I-pictures of a particular sequence must be identified. Picture coding type identifies whether a picture is an intra-coded (I) picture or predictive coded (P) picture or bi-directionally predictive coded (B) picture.
In order to do this today, current transport processors must parse and evaluate every bit in each received transport packet payload to determine the presence of a picture start code, which is a string of 32 bits that are set to (00 00 01 00h). This is both time-consuming and unnecessary, and is a substantial drain on processing power. Once the picture start code is detected, only then will the transport processor evaluate and identify the picture coding type.
As noted, this individual parsing and evaluating of each bit in each transport packet payload unduly delays programming, causes user frustration, and places an unnecessary burden on the processing capability of the DVR system. Therefore, what is desired is a method and apparatus for identifying the MPEG picture coding type without having to parse and evaluate each bit in each DSS transport packet.